The field of the invention is substituted 1,3-diols and the invention is particularly concerned with the purification of these diols.
An Example of these 1,3-diols is trimethylpentanediol (2,2,4-trimethyl-1,3-pentanediol) as disclosed in the Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 10 (1966) pp. 676-680 and the Kirk-Othmer, Concise Encyclopedia of Chemical Technology (1985) under the section "Other Glycols", p. 568. Other substituted 1,3-diols are disclosed in U.S. Pat. No. 2,643,262 such as ethylhexanediol (2-ethyl-1,3-hexanediol), and propylheptanediol (2-propyl-1,3-heptanediol).
The state of the art of purifying these substituted 1,3diols may be ascertained by reference to U.S. Pat. No. 2,865,819, West German Pat. No. 967,552 and Japanese Pat. No. 69/10767, the disclosures of which are incorporated herein by reference.
In the present invention the term saponification number is used and this term is defined in Kirk-Othmer, supra, Vol. 1 (1963) at page 302 as the number of miligrams of potassium hydroxide required for the saponification and neutralization of one gram of sample.
The substituted 1,3-diols of the present invention have the general formula: ##STR1## where R=alkyl and/or hydrogen, R'=alkyl.
These substituted 1,3-diols of the general formula are prepared by aldolization reactions with ensuing hydrogenation according to the following equation: ##STR2##
Frequently esters are obtained as by products in the above reaction which must be removed by distillation separation. Product losses are incurred in this distillation separation and the separation requires a more than proportional cost.
Esters are saponifiable in principle but new problems arise in crude products so treated. These problems include partial product decompositions during distillation. Japanese Pat. No. 69/10767 recommends using extractants such as di-n-butylether in the case of water-soluble 2,2-dimethyl-1,3-propanediol to avoid these problems. Again, pretreatment by means of a falling-film evaporator is recommended to separate salts and substances of higher boiling points accumulating during the synthesis. In the process of U.S. Pat. No. 2,865,819, water and tetralin are added to separate neopentyl glycol from the saponification salts in several stages. Further, West German Pat. No. 967,552 discloses using ion exchangers to remove salts contained in the crude product.
Some of the drawbacks of these methods are that they require accessory substances which must be removed in energy-intensive manner and/or which are expensive or leave out of consideration losses of valuable materials.